The short answer is that, while population studies do often find that a diet lower in animal products is usually lower in saturated fat and cholesterol and results in lower serum cholesterol levels and less coronary artery disease, such population studies cannot demonstrate causation. They must be interpreted with caution because of confounding variables. For example, vegetarians are more likely to be more affluent and more active than non-vegetarians. They are also less likely to smoke or drink heavily. So it may be these other variables, rather than simply the avoidance of animal products, that leads vegetarians to be healthier on average than those that eat meat.
A study of Seventh Day Adventists (SDA) by Dr. Fraser and colleagues at Loma Linda University was published in the June 2013 Journal of the American Medical Association of Internal Medicine and got around some of these confounding factors by focusing on a population of people in which the more vegetarian subjects were not much different in regard to these other confounding variables. This study measured what the subjects were eating, put them in various "vegetarian" groups, and then observed them over a 6 year period, comparing their relative risk of cardiovascular disease (CVD) and total mortality to non-vegetarian SDA subjects who also had a similar healthful lifestyle. The groups were classed as "vegan", "semi-vegetarian", "pesco-vegetarian", "lacto-ovo-vegetarian", and "non-vegetarian". On the surface, it seems like a very interesting study examining the impact in SDA subjects of eating these various "vegetarian" diets compared to SDA subjects who ate meat regularly. The results showed that the "vegetarians" were less likely to die (particularly from CVD) than the meat eaters. The relative risk of dying over the next 6 years was 15%, 8%, 19%, & 9% less, respectively for the various "vegetarian" groups than it was the non-vegetarians (1). Sadly, the authors failed to tell us what criteria were used for putting people in these various groups, and they provide no data about the nutritional breakdown of what these various groups actually ate.
There is little reason to believe that avoiding all or most animal foods is not the key to a healthful overall diet -- it can move people away from many of the foods in a typical modern diet that raise LDL-C levels in the blood and promote more atherosclerosis. A strict vegan diet would have no cholesterol and likely be much lower in saturated fat than a diet high in fatty animal products. However, vegan diets are also lower in vitamin B-12 and can result in higher homocysteine levels. Higher homocysteine levels have been associated with more CVD and Alzheimer's disease. Vegan diets also tend to be lower in long chain omega-3s, calcium, zinc, and iron than diets containing animal products. What is clear is that a vegan and/or vegetarian diet, in and of itself, does not automatically equate to a healthful diet. Regardless of whether or not some or all animal products are eliminated from one's diet, the principles of a healthful diet remain the same. Eliminating all animal products alone is certainly not a clear-cut way to assure one's diet is healthful, nor is a more vegetarian diet alone the key to optimal health. A vegan diet will eliminate cholesterol, as this dietary insult comes only from animal foods. However, a vegan diet will not necessarily be of much value for preventing even high cholesterol levels and CVD. Why? Because a vegan diet could still be high in saturated fat or trans fats if the vegan choses to consume a lot of coconut oil or partially hydrogenated vegetable oils. So even a vegan diet could provide large amounts of cholesterol-raising fats. A lacto-ovo-vegetarian diet could easily be even higher in saturated fat and cholesterol than one with more meat and less fatty dairy products and eggs. A vegetarian diet may be just as high or higher in added salt as a typical American diet and may be even higher in refined grains and sugars than a diet with few or no animal products. And even if a healthful, more vegetarian diet is consumed, that alone cannot assure optimal health. Why? Other lifestyle-related factors such as inactivity, tobacco smoke, and excessive alcohol consumption will all undermine health and promote disease even if one is following a healthful diet low in salt, "bad" fats, cholesterol, and refined carbohydrates.
A 2006 review by Dr. Appleby compared the health effects of vegetarian and vegan diets and found that while vegans weighed a bit less on average and had lower serum cholesterol levels, they were also more likely to have low intakes of vitamin B12, calcium, and omega-3 fatty acids and on average have higher serum homocysteine levels. In addition, while the vegetarians had a slight reduction in mortality from heart disease, there was no significant difference in cancer rates and little difference all-cause mortality (2).
Bottom Line: A typical modern diet is likely to contain far too much saturated fat and cholesterol for optimal health. Most or all of these atherogenic dietary components typically come from animal products. So cutting back on fatty dairy products, eggs, and meats is generally a step toward a more healthful diet. However, switching to nonfat dairy and egg whites is likely to be more healthful than replacing fatty dairy products with processed foods rich in refined grains and/or sugars. A healthful diet can certainly contain small amounts of foods like omega-3 rich seafoods, nonfat dairy, and egg whites. In addition to avoiding foods high saturated fat, trans fat, and cholesterol, it is also important to avoid too much salt, refined carbohydrates, and refined fats and oils. Calorie-dense, nutrient-poor foods promote obesity and other metabolic ills, even if they contain nothing from an animal.
By James J. Kenney, PhD, FACN
- doi: 10.1001/jamainternmed. 2013. 6473?2.
- Proc Nutr Soc. 2006 Feb; 65(1): 35-41
Stephanie Ronco has been editing for Food and Health Communications since 2011. She graduated from Colorado College magna cum laude with distinction in Comparative Literature. She was elected a member of Phi Beta Kappa in 2008.